The application relates to a plastics-based composite material for prosthesis purposes, which contains fillers of high X-ray absorption, based on glassy or glass-ceramic systems.
Plastics-based composite materials (or composites) have gained increasing importance in the recent past. Additions of inorganic fillers to polymerizable organic binders not only reduce shrinkage on polymerization, but also improve the mechanical strength data such as, for example, the compressive strength, the flexural strength and the modulus of elasticity. At the same time, the co-efficient of thermal expansion of the composite is also reduced as compared with that of the pure plastics.
The total composite system can be provided with the specific properties of the particular fillers used by the addition of inorganic fillers to organic binders. Thus, for example, in polymethyl methacrylate (PMMA) which is used for prothesis purposes, it was possible to transfer the property of forming a bond free of connecting tissues between bioactive implant material and bones to this system by introducing bioactive glass ceramics in a granular form into the PMMA; in this connection, compare German Pat. No. 2,501,683.
Furthermore, U.S. Pat. No. 3,066,112 has disclosed, in plastics-based dental materials, the replacement of methyl methacrylate by the reaction product of glycidyl methacrylate and bisphenol A, namely bis-[4-(2-hydroxy-3-methacryloyloxypropoxy)-phenyl]-dimethylmethane (also called bis-GMA) and the addition of quartz powder, treated with a vinylsilane, as an inorganic filler.
If the chemical composition is suitable, the inorganic filler can also be used for providing the plastics, which by their nature are permeable to X-rays, with the property of X-ray absorption, so that they become visible on the X-ray film. U.S. Pat. No. 3,539,526 has disclosed the use of a finely particulate glass prepared from SiO.sub.2, BaF.sub.2, AL.sub.2 O.sub.3 and B.sub.2 O.sub.3 as a radiopaque additive in tooth-filling material. These fillers frequently contain a high proportion of barium; however, their X-ray absorption is not sufficiently high for employing them successfully in composite materials which are used in the posterior tooth region. Known composites with barium-containing fillers reach a radiopacity of about 200%.
In addition, radiopause glasses are also known, the X-ray absorption of which is provided by the addition of compounds of strontium and lanthanum or of strontium or tungsten, cf. German Offenlegungsschrift No. 2,458,380. However, the X-ray absorption of even these glasses is not sufficiently high for using them in the preparation of a composite material of sufficiently high radiopacity for the posterior tooth region.